Method and apparatus for screen printing

Abstract

When a printed circuit board is inspected and determined to have an insufficient amount of printing of a print pattern, the printed board is returned to a screen-printing apparatus so that a new print pattern is formed so as to overlap a previous print pattern. In the re-printing, a raising speed of the printed board at a final stage of the board raising operation is rendered lower than in the previous screen printing so that the printed board is brought into contact with the underside of the screen mask more slowly.

1. A screen-printing method in which a circuit board transferred below a screen mask is raised to be retained in contact with an underside of the screen mask, and a squeegee brought into contact with an upper surface of the screen mask is moved so that the circuit board is screen-printed, the method comprising:
 raising a previously printed circuit board (hereinafter referred to as “printed board”) thereby to bring the printed board into contact with the underside of the screen mask when the printed board is to be screen-printed again so that a print pattern is formed so as to overlap a previous print pattern, wherein a raising speed of the printed board at a final stage of the printed board raising operation is rendered lower than in the previous screen printing so that the printed board is brought into contact with the underside of the screen mask more slowly, 
 wherein a mask support plate located at a side of the printed board is raised thereby to be brought into contact with the underside of the screen mask before the printed board is brought into contact with the underside of the screen mask and subsequently, the printed board is raised to be brought into contact with the underside of the screen mask, and the squeegee is brought into contact with the upper surface of the screen mask so that the screen mask is held between the squeegee and the mask support plate. 
 
     
     
       2. The method according to  claim 1 , wherein when the mask support plate located at the side of the printed board is raised into contact with the underside of the screen mask in the re-printing, the mask support plate and the printed board are raised so that the mask support plate is brought into contact with the underside of the screen mask while the mask support plate is located higher by a predetermined dimension than the printed board, and subsequently, the raising speed of the printed board is reduced so that the printed board is brought into contact with the underside of the screen mask more slowly. 
     
     
       3. The method according to  claim 2 , wherein in the re-printing, the raising speed of the printed board is reduced after a predetermined period of time from the contact of the mask support plate with the underside of the screen mask, so that the printed board starts to be brought into contact with the underside of the screen mask more slowly. 
     
     
       4. A screen-printing apparatus comprising:
 a screen mask; 
 a unit which raises a circuit board transferred below the screen mask thereby to hold the circuit board in contact with an underside of the screen mask; 
 a squeegee which is moved while being in contact with an upper surface of the screen mask so that the circuit board is screen-printed; and 
 a control unit which controls a raising operation of the circuit board transferred below the screen mask, the control unit controlling the screen-printing apparatus so that when a previously printed circuit board (hereinafter referred to as “printed board”) is to be screen-printed again so that a print pattern is formed so as to overlap a previous print pattern, the printed board is raised thereby to be brought into contact with the underside of the screen mask, and so that a raising speed of the printed board at a final stage of the printed board raising operation is rendered lower than in the previous screen printing so that the printed board is brought into contact with the underside of the screen mask more slowly, 
 wherein the control unit controls the screen-printing apparatus so that a mask support plate located at a side of the printed board is raised thereby to be brought into contact with the underside of the screen mask before the printed board is brought into contact with the underside of the screen mask, and the squeegee is brought into contact with the upper surface of the screen mask so that the screen mask is held between the squeegee and the mask support plate and subsequently, the printed board is raised to be brought into contact with the underside of the screen mask. 
 
     
     
       5. The screen-printing apparatus according to  claim 4 , wherein the control unit controls the screen-printing apparatus so that when the mask support plate located at the side of the printed board is raised into contact with the underside of the screen mask in the re-printing, the mask support plate and the printed board are raised so that the mask support plate is brought into contact with the underside of the screen mask while the mask support plate is located higher by a predetermined dimension than the printed board, and subsequently, the raising speed of the printed board is reduced so that the printed board is brought into contact with the underside of the screen mask more slowly. 
     
     
       6. The screen-printing apparatus according to  claim 5 , wherein the control unit controls the screen-printing apparatus so that in the re-printing, the raising speed of the printed board is reduced after a predetermined period of time from the contact of the mask support plate with the underside of the screen mask, so that the printed board starts to be brought into contact with the underside of the screen mask more slowly.